1. Field of the Invention
The present invention relates to horology and, in particular, to methods and devices for time measurement using an electrical time base. Still more particularly, the present invention provides a device, which may be a solid-state device, with methods and systems pertaining thereto, for measuring time without an oscillator, oscillating element, or oscillating circuit and without a continuous power source.
2. Description of Related Art
Portable electronic devices have become ubiquitous, and as the size and cost of electronic circuits continues to be reduced, electronic devices continue to be incorporated in an increasing number of consumer products. As an example, paper greeting cards that play music when opened are no longer considered a novelty. Technical progress has been made on flexible circuits that will allow electronic circuits to created in a variety of shapes and to be embedded into more products.
Inexpensive electronic devices can be categorized based upon their power requirements or associated power systems. Some electronic devices have a variety of functions that may require the device to be powered by an external power source, such as an electrical outlet via an AC-DC adapter, while some devices require one or more batteries. Other devices may require both types of power sources: an external power source for enabling most functions, and a small battery for powering minor functions, such as a clock or timekeeping function, while not connected to an external power source or while xe2x80x9cturned offxe2x80x9d. Small electronic devices frequently incorporate a small, flat battery, similar to those that power electronic watches, merely to power a clock circuit. Generally, the battery powers some type of time base oscillator or pulse generator that measures the passage of units of time.
The incorporation of a battery into an electronic device solely for a simple clock function creates several disadvantages. Chemical batteries present potential chemical leak and disposal hazards and are relatively expensive compared to the cost of fabricating a tiny electronic circuit. Batteries tend to have a short shelf life, especially compared to the useful life of the electronic circuits that they accompany. In addition, batteries are sometimes several times larger than the electronic circuit to which they are connected, thereby placing design restrictions on the electronic device.
Electronic time base oscillators are assumed to be necessary for small, electronic, horological devices, but the accompanying batteries have many inherent disadvantages. Hence, the current state of technology constrains the conception of other devices, consumer products, or consumer services that might incorporate a time measurement function.
Therefore, it would be advantageous to provide a tiny, simple, electronic, horological device that provides time measurement without a battery or an oscillator.
A simple electronic horological device, termed a time cell, is presented in addition to associated methods, systems, devices, and computer program products. The claims of the present application are mostly directed to a particular type of time cell and the devices and their associated methods that may be used to read the time cell, thereby generating a time measurement that may be used for a temporally dependent purpose.
A time cell includes an insulated, charge storage element that receives an electrostatic charge through its insulating medium, i.e. it is programmed, thereby giving the charge storage element an electric potential with respect to points outside the insulating medium. Over time, the charge storage element then loses the electrostatic charge through the insulating medium. Given the reduction of the electric potential of the programmed charge storage element at a substantially known discharge rate, and by observing the electric potential of the programmed charge storage element at a given point in time, an elapsed time period can be determined. Thus, the time cell is able to measure an elapsed time period without a continuous power source.
One type of time cell is an analog time cell that may have a form similar to a non-volatile memory cell, such as a floating gate field effect transistor (FGFET). The analog time cell may have an expanded floating gate for storing an electrostatic charge. At a given point in time after programming the analog time cell, a sensing operation indirectly observes the retained charge in the floating gate by directly or indirectly observing the threshold voltage of the FGFET. By knowing the operational characteristics of the analog time cell and its initial programming condition, the observation can be converted into an elapsed time value. A time cell can be designed and/or programmed to select the range of time to be measured by the time cell.